There has been typically used a buckle that detachably engages a plug with a socket in order to couple a string member such as a belt in various applications such as clothes, bags, shoes and packages.
Such a buckle is required to be easily handled for coupling and releasing and not to cause an accidental release when the buckle is not intended to be released. As a product responding to such needs, a side release buckle including a pair of lock arms on both sides thereof has been used.
For instance, a side release buckle disclosed in Patent Literature 1 includes a plug and a socket, each of which is provided with a belt attachment.
The plug includes a base including the belt attachment and a pair of legs (lock arms) on both sides near the socket. The socket includes a hollow cylindrical body, which has a housing space (cavity) into which the plug is inserted through an insertion opening facing the plug.
Engaging portions formed at tip ends of the lock arms are engaged with engaged portions formed deep inside the housing space to maintain a coupling between the plug and the socket.
A pair of guide surfaces are formed on the inner surface of the housing space (the inside of the top and bottom surfaces of the socket), and extend from the insertion opening to the engaged portions while being opposed to each other so as to guide the engaging portions inserted through the insertion opening to the engaged portions.
The pair of guide surfaces, each of which is defined in a step on the inner surface of the socket, are linearly continuous from the insertion opening to the engaged portions. The pair of guide surfaces have an interval in a tapered shape therebetween, the interval being wider near the insertion opening and narrower near the engaged portions.
When tip ends of the plug are inserted into the socket through the insertion opening, the lock arms are smoothly guided into the housing space by the pair of guide surfaces. Subsequently, when the plug is pressed deep inside, the pair of engaging portions formed at the tip ends of the lock arms are squeezed in a direction to approach each other by the pair of guide surfaces while being guided to smoothly fit in the engaged portions. In this manner, the engaging portions can be easily and reliably engaged.
An opening in communication with the housing space is formed on each side of the body of the socket. The engaging portions and the engaged portions can be disengaged by manipulating the legs exposed through the openings by fingers.
In such a side release buckle, the plug and the socket each are integrally formed mainly of a synthetic resin material. Accordingly, while the legs are provided with a predetermined elasticity, the plug, the socket and the belt attachment of each of the plug and the socket are provided with a sufficient strength to resist tension of the coupled belt in use.